1. Field of the Invention
The invention relates to a method for operating recursive filter circuits or analog storage circuits constructed according to the charge coupled device (CCD) principle and to a circuit arrangement for implementation of the method in which only each respective second storage of a CCD is occupied with a charge representing a sampling value of an analog signal and the stages respectively lying between these stages concerned are left empty.
2. Prior Art
Know recursive filter circuits constructed according to the CCD principle conduct the signal from the output stage of a CCD chain to the input of the CCD loop via an amplifier to which the input signal is simultaneously supplied, c.f., for example, IEEE Journal of Solid State Circuits SC-7 (1972) October, pages 421 through 425; SC-8 (1973) April, page 157; Conference volume of the CCD 74, Edinburgh: "Signal Processing Application of Charge-Coupled-Devices" and "MTI Filtering for Radar with CCD"; 6th International Congress of Microelectronics: "Charge-Coupled-Devices". So that a good filter effect is achieved, the amplification must amount to 1 very precisely. Namely, given amplification that is too low, the quality of the filter would be too low, given amplification that is too high, self-oscillation would occur.
According to the present state of knowledge, an amplifier of the necessary high stability which is arranged in common on a chip with the CCD concerned cannot be satisfactorily realized.
It has been proposed that the critical amplifier be eliminated. To that end, it has been proven that, in principle, no amplifier is required in a CCD loop because the low transmission losses given CCD's allow one to expect a sufficiently high quality of the filter circuit. If one allows an information to circulate in a closed CCD loop, then the problems resulting from an amplifier of high stability are eliminated. However, such a CCD loop is not functional over a long time without additional devices, since the potential troughs of the individual stages become filled with charge carriers which derive from inverse currents and incomplete charge transfer. Therefore, it must be seen to, with an auxiliary circuit, that these parasitic charges are again removed and, thus, the operating point of the CCD loop is retained. The operating point is defined by the charge amount in the potential troughs in the idle state of the stages.